4. The Beatles

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It's really not possible to overstate the Beatles' significance. They're the best-selling group in the history of American music, Rolling Stone's greatest artist of all time, and, inexplicably, The Beatles: Rock Band (released last month) is enjoying robust sales among a generation that wasn't even born when the group broke up. Their immense, unprecedented popularity neatly coincides with the decade (they adopted their name in 1960 and disbanded in 1970), leaving their body of work as an immensely successful, groundbreaking, iconic statement on the atmosphere and social climate of the time period.